Zepto SDE-1 Interview Experience

Round 1: DSA and Code Evaluation

Problem Statement:

You are given two arrays, arrival and departure, representing the arrival and departure times of trains at a railway station.

Your task is to find the minimum number of platforms required so that no train has to wait for a platform. A platform cannot be assigned to another train until the current train has departed.

If a train arrives at the same time another train departs, a separate platform is required for the arriving train.

Example:

Input:

arrival = [900, 940, 950, 1100, 1500, 1800]

departure = [910, 1200, 1120, 1130, 1900, 2000]

Output: 3

Explanation:

At certain times, three trains are present at the station simultaneously. Therefore, at least three platforms are required to accommodate all trains without delays.

2. Code Evaluation and Test-Case Generation

The second part involved reviewing code written in Java or Go that contained incorrect logic.

The task was to understand what the code was intended to do, identify scenarios where it could fail, and prepare test cases using an LLM. The code also involved concurrency-related behaviour, so the tests needed to consider potential issues arising from concurrent execution.

The expected workflow was:

• Understand the existing code and explain its purpose and logic to the interviewer.

• Write test cases in plain English before prompting the AI agent.

• Record every prompt verbatim and in order in the same document.

• Ask the agent to implement the test cases and run them.

• Observe the failures, identify the underlying issue, and fix the code either independently or with the agent.

• Run the tests again and demonstrate that they pass.

The focus was on reasoning, testing, debugging, and understanding concurrent code rather than simply generating code with AI.

Round 2: Low-Level Design (LLD)

The LLD round involved designing a Splitwise-like expense-sharing system.

The main requirements included:

• Create and manage group expenses.

• Record expenses between individual users.

• Allow users to view both direct and group expenses.

• Update an existing transaction.

• Support basic Create, Get, and Update operations.

The discussion focused on structuring the system and designing the necessary entities and operations to support these requirements.